It may be a sweltering July, but you get the sense that “Fela!” would have the sweatiest cast on Broadway no matter the season. These guys work so incredibly hard that they’re glistening with perspiration within five minutes. The energy stays in the red for the entire frenzied first act of the 2009 Tony-nominated musical, now back for a brief summer engagement.

Indeed, if this biomusical about the late Nigerian pop star and political activist Fela Anikulapo Kuti ended at intermission, it would be just about perfect.

But it doesn’t — and the second act is a puzzling hodgepodge that doesn’t quite know what to do with itself.

Directed and choreographed by Bill T. Jones, who wrote the book with Jim Lewis, the show has a simple conceit: Surrounded by his faithful band and dancers, Fela (original cast member Sahr Ngaujah, or Adesola Osakalumi at select performances) is giving one last concert at his Lagos club, the Shrine, after the death of his mother, Funmilayo (Melanie Marshall).

A charismatic ringmaster, Fela reflects back on his invention of the driving music known as Afrobeat and on his political awakening — which comes when this notorious womanizer meets a sexy American supporter of Black Power named Sandra (Paulette Ivory).

The book smoothly integrates biographical elements and musicianship into the numbers, and even a prolonged bit of audience participation earns its place — this is meant to evoke a concert, so it makes sense to invite people to stand up or sing along.

But the second act remains as much of a problem as it was during the show’s initial Broadway run, and even the tireless Ngaujah can’t save it.

Jones must have realized that he couldn’t have 2 1/2 hours of ferocious, horn-laden Afrobeat hits like “Everything Scatter” and “Zombie,” but he didn’t find a satisfying way to break things down.

So the politics are awkwardly folded into the plot, and the ghostly presence of Funmilayo becomes disruptively distracting.

Marshall — like Ivory, an alum from the National Theatre production in London — brings a fantastic operatic voice to “Rain,” the song at the heart of an extended dream sequence. But there’s little she can do with the character, because there’s no character to speak of: Only Fela is given a full portrait, and everybody else is a sketch.

Too bad Jones couldn’t figure out the slower patches, because when it’s at full speed, “Fela!” is just about unstoppable.